Laminated cellulosic fabrics



rue-14 iatenteci Oct.

UKUDS KtI'hKLNUlZ LAMINATED CELLULOSIC FABRICS Richard H. Wiley, Wilmington, DeL, assig'nor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 22, 1945, Serial No. 574,040

sealing cardboard containers, is well known. When sodium silicate is used by itself the bond formed suffers from the disadvantage of being very moisture-sensitive, and under conditions of high humidity or water immersion it fails rapidly and permits the separation of the surfaces originally joined by the bond.

This invention has as an object the provision of an improved paper product. A further'object is the preparation of an improved paper-to-paper bond in laminated paper products. A still further object is the preparation of an improved laminated paper article, said laminated article being resistant to separation into its component laminae when subjected to moisture. Still another object is the preparation of an improved paper-to-paper bond using a sodium silicate adhesive. A further object is the preparation of a moisture-and-water-resistant paper to paper bond using sodium silicate as the adhesive. A still further object is a treated paper which can be readily bonded by means of sodium silicate to form a composite body or sheet which is resistant to separation into its component parts in water or under conditions of high humidity. Additional objects will become apparent from an examination of the following description and claims.

These and other objects and advantages are accomplished according to the herein described invention which broadly comprises applying to the surface of a paper a 1% to by weight aqueous solution of a fluosilicate of magnesium or zinc, drying the paper, applying an aqueous sodium silicate solution to the fiuosilicate-treated surface thereof and pressing the resultant coated surface to another similarly coated surface to I form an adhesive bond between the surfaces.

In a preferred embodiment of this invention a paper product, e. g., a highly sized Kraft paper or a slack sized corrugating paper, is treated with an aqueous solution of from 2.4% to 10% by .weight of magnesium fluosilicate and dried. The surface of the treated paper is then further coat- -ed with an aqueous solution of a sodium silicate adhesive and the surface of the paper bearing the adhesive is pressed against a similarly treated paper surface and set under the influence of heat. The adhesive bond thus formed remains strong over a long period of time under conditions of high humidity and even under conditions of water immersion, whereas a bond formed with sodium silicate on untreated paper or paper board fails in a relatively short time under these same conditions.

The following description and examples, in which proportions are in parts by weight unless otherwise specified, are given for illustrative purposes and are not intended to place any restrictions on the herein described invention.

Samples for testing were prepared from 3" x 3" squares of paper which were conditioned at 20% relative humidity for at least 24 hours prior to the preparation of the adhesive bond. Immediately after the removal of the paper from the conditioning apparatus the paper was treated with the aqueous fluosilicate solution and dried. A sodium silicate adhesive was then spread on the rough finish side of the paper in 2 uniform lines of adhesive about and 1 in., respectively, from one end of the sheet of paper. The adhesive lines were applied perpendicular to the grain (machine) direction. This paper with the adhesive line spread on it was then placed on a steam heated hot plate at a temperature of 130- 135 C. and the corresponding edge of the second 3 in. square was placed so as to lap over the adhesive lines. A 2.2 kg. weight measuring 1% x 3 in. on the bottom was then placed over the area where the glue lines had been located. After 10 seconds had elapsed, the weight was removed and the sample taken from the hot plate and placed in a relative humidity atmosphere for 24 hours prior to testing. This technique was used in preparing samples of highly sized Kraft and slack sized corrugating types of paper.

Example I A slack-sized 9-point Kraft corrugating medium paper weighing 25 lbs/1000 sq. ft. with a 215-230% water pick-up as determined by the method given in Federal Specification l5-FSC- 1539-D and having a dry Mullen test of lb. and a wet Mullen test of 14 lb. was immersed in a 6% (based on anhydrous salt) magnesium fluosilicate aqueous solution and dried. The paper contained about 5.8 lb. of magnesium fiuosilicate per 1000 sq. ft. An adhesive-type sodium silicate solution having a l/3.25 weight ratio of NazO/SiOz,

a gravity of 405 Baum, and 36.1% solids was applied to one sheet of this treated paper in accordance with the above-described procedure and a second sheet of magnesium fluosilicate treated UBM paper of the same type was bonded by the sodium silicate adhesive to the first sheet. The bond resulting remained strong even after 60 days immersion in water. A control bond prepared with the same sodium silicate adhesive on the same paper which was not treated with magnesium fluosilicate fell apart in less than 5 minutes immersion in water.

When a 2.4% aqueous solution of magnesium fluosilicate was used to treat the paper prior to the bonding with the sodium silicate adhesive, a bond was obtained which was still strong after 40 days immersion in water. when aqueous solution of as little as 1.2% magnesium fluosilicate was used to treat the paper prior to the bonding with the sodium silicate adhesive, a paper was obtained containing slightly more than 0.5 lb. of magnesium fluosilicate per 1000 sq. ft. and the bond was still strong after 24 hours immersion in water.

- Example II A highly alum-rosin sized 25 point Kraft paper weighing 92-95 lbs/1000 sq. it. having a dry Mullen test of 122 lb. and a wet Mullen test of 34 lb. with a 61% water pick-up (as determined by the method given in Federal Specification -FSC- 1539-D) was brushed with a 6% (based on anhydrous salt) magnesium fluosilicate aqueous solution and dried. The paper contained about 2 lb.

Example III Two 3" x 4" samples of single face B-flute corrugated paper board bonded with waterproof and nonwaterproof starch adhesive, respectively, were conditioned at relative humidity for at least 24 hours. The exposed flutes of the corrugated paper board were then brushed with a 10% (based on anhydrous salt) magnesium fiuosilicate aqueous solution and dried. A Kraft paper of the type described in Example 11 was brushed with a corresponding solution of magnesium fluosilicate and dried. The tips of the exposed flutes of the corrugated paper board were brushed with a. sodiumsilicate adhesive solution as described in Example I. The Kraft liner was then bonded to the flutes by placing the fluted side against the treated Kraft paper which was in contact with a steam heated hot plate at a temperature of ISO-135 C., and the laminated sample was covered with a thin board on which a 2.5 kg. weight was placed for 10 seconds to set the adhesive. The assembly was then conditioned at relative humidity prior to testing. A strong bond was obtained with both the samples of corrugated paper board which bond remained stron even after 96 hours immersion in water. In control samples which were untreated with the magnesium fluosilicate solution a bond prepared with nonwaterproof starch as the adhesive failed after 5 minutes immersion in water. A similar control sample prepared with waterproof starch as the adhesive iailed after about 3 hours under'these conditions. Samples prepared using corrugated paper board and Kraft paper which had not received the prior treatment with magnesium fluosilicate, and in which sodium silicate was used as The bond thus formed remained,

the adhesive failed after about 3 hours immersioninwater.

Samples of corrugated paper board and Kraft paper prepared as above which were treated with 6% aqueous magnesium fluosilicate and bonded with sodium silicate were still strongly bonded after 14 days exposure to high humidity in a closed vessel over water. The bond was markedly stronger than that in an untreated control sample bonded with waterproof starch and exposed to high humidity for the same length of time under the same conditions.

Example IV A sample of slack sized paper as described in Example I which was treated with a 10% aqueous solution of zinc fluosilicate and bonded with sodium silicate solution as described in Example I showed no failure of the bond when immersed in water for 60 days.

The metal i'luosilicate must be applied to the surface of the paper in the form of an aqueous solution. Said solution may contain from 1% to 10% by weight (calculated as anhydrous salt) of the metal fluosilicate; while for optimum results said solution should contain from 2.4% to 10% by weight of said salt, Said solution may be applied to the paper by immersion, by brushing, by spraying o by contacting the paper surface with an absorbent material containing the solution of the metal fiuosilicate. The treated paper may then be dried at room temperature, e. g. 25 C., or at elevated temperatures before subsequent application of the sodium silicate adhesive. The fluosilicate-treated paper may be used immediately for bonding with sodium silicate or said paper may be stored indefinitely for use at a later period.

Irrespective of the method of application of the fiuosilicate solution to the paper, said solution should be added in a quantity sufficient to provide a paper containing metal fluo silicate (calculated as anhydrous salt) in an amount equivalent to not less than 0.5 lb. per 1000 sq. ft. of

2 treated paper and, in any event, in an amount equivalent to not less than 1% by weight of the paper treated. The optimum amount of metal fluosilicate will depend to a great extent on the degree of sizing of the paper to be treated. Thus, with a highly sized paper containing from 2 to 4% by weight of an alum-rosin size, sufiicient fiuosilicate should be added to provide a paper containin said fluosilicate (calculated as anhydrous salt) in an amount equivalent to not less than one pound per 1000 sq. ft. of treated paper and also in an amount equivalent to not less than 1% by weight of the papertreated. On the other hand, with a slack sized paper containing less than 2% by weight of an alum-rosin size, sufficient fluosilicate should be added to provide a paper containing said fluosilicate (calculated as anhydrous salt) in an amount equivalent to not less than one-half pound per 1000 sq. It. of treated paper and, also, in an amount equivalent to not less than 2% by weight of the paper treated. In any event, the treated paper should contain not morethan 10% by weight of metal fiuosilicate (calculated as anhydrous salt) since the use or more than 10% of said fiuosilicate apparently has little further beneficial effect on the properties of the resultant paper, 1'. e. gives little further improvement in forming a water-resistant bond with sodium silicate adhesives.

The sodium silicate applied to the fluosilicatetreated paper surface is, of course, applied therevnuoo nLr LKLHLIL to as an aqueous solution, e. g. by the method disclosed at pages 210-251, Chapter VIII, Vails Soluble silicates in Industry, published 1928 by the Chemical Catalogue Co. of New York. It is to be understood, of course, that said sodium silicate may be applied to the paper by any convenient method, as by immersion, by brushing, by spraying or by contactin the paper surface with an absorbent material containing the solution of the sodium silicate. Bonding of the duosilicate-coated surfaces may be effected in any convenient manner, as by pressing the treated surfaces together and heating the same, References to this type of bonding are to be found, for example, at page 226 of the aforementioned publication of Vail.

It is to be understood that my process is applicable to fibrous cellulosic fabrics broadly, e. g. paper, cloth, rope, cord, wood and the like. However, said process is particularly well adapted to the treatment of non-woven fibrous sheeted cellulosic fabrics, especially paper products such as paper and paper board. Thus, this invention provides a method for obtaining laminated paper, and corrugated paper board which do not delaminate or separate after long periods of immersion in water. This is of particular advantage in the preparation of corrugated paper containers which are subjected to conditions of high humidity or to immersion in water. Although this invention is of particular use with paper and paper articles of cellulosic fibers, it is also applicable to non-woven sheeted articles of other fibrous materials, for example, asbestos.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the drous salt, of said fiuosilicate and being applied in such amount that the paper product contains at least 0.5 lb., calculated as anhydrous salt, of the said fiuosilicate per 1000 sq. ft. of surface, thereafter drying the said paper product, applying an aqueous sodium silicate solution to the metal fiuosilicate-treated surface thereof and pressing the resultant coated surface against a paper surface treated in the same manner as the first sheet with a compound from the group consisting of magnesium fiuosilicate and zinc fiuosilicate to form an adhesive bond between the surfaces.

2. In a process for obtaining paper products having surfaces adhesively joined together, the steps of app y n to a surface of a paper product an aqueous solution of magnesium fiuosilicate,

said solution containing from 2.4% to 10% by weight, calculated as anhydrous salt, of said fiuosilicate, thereafter drying the paper product, applying an aqueous sodium silicate solution to the magnesium fiuosilicate-treated surface thereof and pressing the resultant coated surface to another surface coated in the same manner as the first sheet with magnesium fiuosilicate to form an adhesive bond between the surfaces.

3. In a process for obtaining paper products having surfaces adhesively joined together, the steps of applying to a surface of a paper product an aqueous solution of zinc fiuosilicate, said solution containing from 2.4% to 10% by weight, calculated as anhydrous salt, of said fiuosilicate, thereafter drying the paper product, applying an aq odium silicate solution to the zinc fluosilicate-treated surface thereof and pressing the resultant coated surface to another surface coated in the same manner as the first sheet with zinc fiuosilicate to form an adhesive bond between the surfaces.

4. As a new article of manufacture a composite paper structure comprising paper laminae, the

. surfaces of which paper laminae are treated with at least 0.5 lb., calculated as anhydrous salt, per 1000 sq. ft. of surface of a salt from the group consisting of magnesium fiuosilicate and zinc fiuosilicate, said treated surfaces being joined together with sodium silicate.

5. As a new article of manufacture, a composite paper article composed of paper products, the surfaces of which are treated with at least one pound, calculated as anhydrous salt, per 1000 sq. ft. of surface of zinc fiuosilicate, said treated surfaces being joined together with sodium silicate.

6. As a new article of manufacture, a composite paper product composed of paper products, the surfaces of which products are treated with at least one pound, calculated as anhydrous salt, per 1000 sq. ft. of surface of magnesium fiuosilicate, said treated surfaces being joined together with sodium silicate.

RICHARD H. WILEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,900,212 Watson Mar. 9, 1933 2,015,359 Carter Sept. 24, 1935 2,128,782 Muller Aug. 30, 1938 2,144,610 Bauer Jan. 24, 1939 2,195,586 Snell Apr. 2, 1940 2,195,587 Snell Apr. 2, 1940 2,349,698 Boller May 23, 1944 FOREIGN PATENTS Number Country Date 2,197 Great Britain 1913 374,298 Great Britain June 9, 1932 488,992 Great Britain July 11, 1938 [Ni- WHHLD 

1. IN A PROCESS FOR OBTAINING PAPER PRODUCTS COMPRISING LAMINAE ADHESIVELY JOINED TOGETHER, THE STEPS OF APPLYING TO A SURFACE OF A PAPER PRODUCT AN AQUEOUS SOLUTION OF A COMPOUND FROM THE GROUP CONSISTING OF MAGNESIUM FLUOSILICATE AND ZINC FLUOSILICATE, SAID SOLUTION CONTAINING FROM 1% TO 10% BY WEIGHT, CALCULATED AS ANHYDROUS SALT, OF SAID FLUOSILICATE AND BEING APPLIED IN SUCH AMOUNT THAT THE PAPER PRODUCT CONTAINS AT LEAST 0.5 LB., CALCULATED AS ANHYDROUS SALT, OF THE SAID FLUOSILICATE PER 1000 SQ. FT. OF SURFACE, THEREAFTER DRYING THE SAID PAPER PRODUCT, APPLYING AN AQUEOU8S SODIUM SILICATE SOLUTION TO THE METAL FLUOSILICATE-TREATED SURFACE THEREOF AND PRESSING THE RESULTANT COATED SURFACE AGAINST A PAPER SURFACE TREATED IN THE SAME MANNER AS THE FIRST SHEET WITH A COMPOUND FROM THE GROUP CONSISTING OF MAGNESIUM FLUOSILICATE AND ZINC FLUOSILICATE TO FORM AN ADHESIVE BOND BETWEEN THE SURFACES. 